Not receiving notification of completed signatures

We are seeing some documents sent out, getting all required signatures, and not sending a copy of the completed process/signed document to the initiator.  How can we be certain that the Adobe server actually sent an email to the initiator?

Note that we are on Exchange in Office 365 and, in general, the initiator gets all copies of completed transactions.

Also, if I go to the "History" for the document, it shows the following at the bottom:

Source: server

**Completed**

If Adobe can show me evidence that the email was in fact sent (left their network), then I can go to our network admins to see if they can track what happened to the email at the border gateway.

Please let me know what information you need in order to track/audit this issue (so, initiator name, time, date, etc.).

Thanks,